Alkalinity

[ox5477]

I've been monitoring my reef stats more closely since started buying coral and my alk has dropped progressivly over the last month from 8.4 to 6.9. Will it naturally migrate as time goes on as the reef matures?

I thought natural seawater was roughly 8.0 so I would want it around there right? or does buffering for other things like calc and mag make the alk vary and go down?

 

[dilbert]

Alkalinity is maybe the only figure someone should keep unnaturally high in a tank.

Seawater is even lower than 8.0 dKH but there is always a huge reservoir of not-depleted seawater (i.e. the entire ocean) and stocking density of this entire ocean is very low. That's not the case in everybody's tank (even if he would have only liverock).

As the alkalinity is sort of a reserve to stablise the ph, I would go for the suggested 8 to 12 dKH. There are often suggested different ranges by different people. The reason is that it depends really on your tank set-up and your stocking density and the livestock itself.

It depends also on the salt your are using as I said that everyone has a different perception about the right range. When I have done excessively many water changes, my alkalinity went down up to 5.6 dKH. That's about the figure of natural seawater.

 

[SkiFletch]

Yup, sounds like calcification to me... As calcifying organisms grow, they consume calcium and carbonate (alkalinity) and both will trend down, even with waterchanges. The only way to keep them up is to dose with suppliments. Like dilbert I prefer to keep my aklalinity high 9-12dKH range. IME, many calcerous orgainsms and corals can tolerate dips in magnesium or clacium, but HATE dips in alkalinity below 7dKH and they're perfectly happy at high alkalinities.

 

[ox5477]

k, sounds like I need to buffer for alk then. Didn't realize it would dip this much. Thought it was predominatly calc and mag they would consume. Thanks for the info guys

 

[SkiFletch]

Yeah, it's an interesting chemical anomoly. Remember, in seawater after sodium and chlorine, the concentration of magnesium is highest, followed by calcium, and lastly carbonate. Yet because corals (or other calcifiers) use these inversely (carbonate most, calcium second, and a drop of magnesium) to make their skeletons, USUALLY alk dips first

 

[kj23502]

Wow! This is fascinating. Good info

 

[SkiFletch]

If I may suggest KJ, since you're obviously reading a lot lately, have a look through the links in the "Realm of Knowledge" sticky atop this section. Lots of great articles and info there to keep your mind going for a long time

 

[kj23502]

Sure Ski, will do!

Thanks